1. Field of the Invention
The present invention relates to an arrangement for applying solid particles to the image carrier of a non-impact printer.
2. Description of the Prior Art
In present day equipment which is used for data processing, greater and greater use is being made of high-speed printers in which characters are printed without relying on raised printing characters impacting on a recipient sheet of paper. Such printing machines, termed non-impact or strike-less transfer printing machines, generally have an image carrier which is usually formed by a rotary drum or an endless belt. The surface of the carrier is formed with sensitized zones or latent images, by electrostatic or magnetic methods. These zones correspond to the characters to be printed and are capable of attracting solid particles of pigment. This carrier is then brought into contact with a recipient sheet of paper to enable the solid particles held by the sensitized zones of the carrier to be transferred to the sheet so that they can be permanently affixed to it.
In the prior art, various particle applicator arrangements have been used to apply solid particles of pigment to the image carrier of a printing machine of this kind. For example, in the application of a powdered pigment to an image carrier formed by an endless belt, use has been made of an arrangement incorporating two pressure rollers between which the endless belt passes. One of the rollers is in contact with pigment contained in a tank to allow the solid particles of pigment to be picked up by this roller as it rotates and deposited on the belt. Such an arrangement has the drawback, however, that it does not always provide an adequate supply of pigment to the belt. Thus, there is a danger that certain sensitized zones of the belt will be devoid of pigment after passing between the pressure rollers.
To ensure an adequate supply of pigment to the image carrier, use has been made of a feed arrangement which incorporates a casing containing the powdered pigment. This casing is provided with an opening across which the image carrier passes. The carrier is supplied with pigment by a cylindrical brush which, rotates within the casing and throws the particles of pigment onto the surface of the carrier as the latter passes across the opening. This arrangement is also not entirely satisfactory in use owing, on the one hand, to the fact that it causes a cloud of pigment particles to be formed which spreads outside the casing, and is particularly unpleasant for people who, being near the printer, come into contact with this cloud, and, on the other hand, to the fact that the particles develop an electrostatic charge and, being thrown onto the carrier, are able to cling to unsensitized zones of the carrier as a result of electrostatic attraction.
In cases where the image carrier of the printer is a magnetic image carrier, use has also been made of pigment supply arrangements formed by a hollow cylinder within which are arranged one or more magnetic cores. This cylinder is positioned close to the image carrier and the pigment, which is composed of a material having magnetic properties, is attracted to the surface of the cylinder by the magnetic field set up by the cores. When the cylinder rotates, the particles of pigment so attracted by the cylinder are carried round with it and, when they come close to the image carrier, are attracted and thereby applied to the magnetized zones of the carrier. The principal drawback of a supply arrangement of this nature is that the image carrier, which passes very close to the hollow cylinder, is inevitably subject to the effect of the magnetic flux generated by the cores which are situated inside the cylinder, so that there is a danger of the information carried by the carrier being severely disrupted. This danger can be reduced by moving the cylinder further away from the carrier, but the distance between the cylinder and the carrier can not exceed a certain limiting value beyond which it is impossible for the carrier to pick up the particles of pigment. As a result, the distance which separates the cylinder from the carrier has to be adjusted with very great accuracy if all the above-mentioned requirements are to be met.